An NADH-Inspired Redox Mediator Strategy to Promote Second-Sphere Electron and Proton Transfer for Cooperative Electrochemical CO2 Reduction Catalyzed by Iron Porphyrin

Abstract

<jats:p>We present a bioinspired strategy for enhancing electrochemical carbon dioxide reduction catalysis by cooperative use of base-metal molecular catalysts with intermolecular second-sphere redox mediators that facilitate both electron and proton transfer. Functional synthetic mimics of the biological redox cofactor NADH, which are electrochemically stable and are capable of mediating both electron and proton transfer, can enhance the activity of an iron porphyrin catalyst for electrochemical reduction of CO&lt;sub&gt;2&lt;/sub&gt; to CO, achieving a 13-fold rate improvement without altering the intrinsic high selectivity of this catalyst platform for CO&lt;sub&gt;2&lt;/sub&gt; versus proton reduction. Evaluation of a systematic series of NADH analogs and redox-inactive control additives with varying proton and electron reservoir properties reveals that both electron and proton transfer contribute to the observed catalytic enhancements. This work establishes that second-sphere dual control of electron and proton inventories is a viable design strategy for developing more effective electrocatalysts for CO&lt;sub&gt;2&lt;/sub&gt; reduction, providing a starting point for broader applications of this approach to other multi-electron, multi-proton transformations.</jats:p>

Proton-Coupled Electron Transfer Catalyst: Homogeneous Catalysis. Application to the Catalysis of Electrochemical Alcohol Oxidation in Water

“…PCET has drawn attention for a long time and more specifically in the past decade for its role in small-molecule activation related to contemporary energy challenges, e.g. water oxidation, O 2 reduction, proton reduction, and CO 2 reduction. , The mechanistic investigation of these processes has triggered an intense development of molecular catalysts that are often transition-metal complexes. Attention has been recently paid to the role of acid or base as a cosubstrate with subtle development of proton relays both experimentally and theoretically, and molecular catalysts are viewed as exchanging electrons with the electrode and then, in a subsequent irreversible step, exchanging a proton with the cosubstrate being an acid in reductive processes or a base in oxidative processes.…”

Through-Space Electronic Conjugation Enhances Co-Electrocatalytic Reduction of CO2 to CO by a Molecular Cr Complex

“…During energy conversion in living cells, chemical bonds are modified by synergistic systems, like the electron transport chain, which achieve high energy efficiency and selectivity by pairing redox-active moieties with metal centers to direct the flow of reducing equivalents. Analogous reactivity has been translated to only one example of homogenous coelectrocatalytic CO2 reduction, 16 while similar reactivity is known for other electrocatalytic reactions. [17][18][19][20] An alternative mechanism for directing electron transfer is through-space electronic conjugation (TSEC), a mechanism of electronic communication between stacked π systems which enables efficient energy and charge transport which has found application in optoelectronic materials and for studying conductance in molecular junctions (Figure 1).…”

Mediated Inner-Sphere Electron Transfer Induces Homogeneous Reduction of CO2 via Through-Space Electronic Conjugation

“…During energy conversion in living cells, chemical bonds are modified by synergistic systems, like the electron transport chain, which achieve high energy efficiency and selectivity by pairing redox-active moieties with metal centers to direct the flow of reducing equivalents. 16 Analogous reactivity has been translated to only one example of homogenous co-electrocatalytic CO2 reduction, 17 while similar reactivity is known for other electrocatalytic reactions. [18][19][20][21] An alternative for directing electron transfer is through-space electronic conjugation (TSEC), a mechanism of electronic communication between stacked π systems which enables efficient energy and charge transport that has found application in optoelectronic materials and conductance studies of molecular junctions (Figure 1).…”